The invention relates to an electronic switch member having one inlet and at least two outlets, and also to the use of such a member to a reconfigurable switch matrix.
For applications that require high reliability, it is common practice to provide redundant electronic elements so that in the event of one of them breaking down, it can be replaced by an identical element. This problem arises in particular for space applications.
To enable a spare element to replace the element that has broken down, it is necessary to provide switching which is controlled either automatically or remotely.
In general, such switching is provided by a matrix having n inlets and p outlets, where the number p of outlets is greater than the number n of inlets. Each of the inlets delivers a signal to an element connected to a corresponding outlet. Thus, only n out of the p possible outlets are normally active. When the element connected to one of the outlets breaks down, then switching is performed so that the corresponding inlet is connected to an outlet having a replacement element connected thereto.
The switch matrices that have been used in the past make use of mechanical switches. An electronic type replacement configuration has yet to be developed that offers advantages comparable to those of mechanical switch matrices. Mechanical matrices give rise to losses that are much smaller than electronic switches; in addition, when not powered, they remain in the switching state they presented before the breakdown. In contrast, electronic switches, in particular in the microwave field, are such that in the absence of power, a portion of the input signal is conveyed to the correct outlet and another portion of the input signal is conveyed to some other outlet for which the signal is not intended. This wrong operation gives rise not only to cross-modulation products that are undesirable, but also to filters heating up. Each outlet corresponds to a frequency range and thus to a filter. If a signal that is not intended for a particular outlet reaches that outlet, then the associated filter reflects the signal, which gives rise to heating.
In a first aspect, the invention thus provides an electronic switch member which minimizes the disturbances to operation of a switch matrix of which it forms a part in the event of the power to said member being absent.
According to the invention, the electronic switch member is for connecting an inlet to one out of a plurality of outlets, and the switch member comprises:
for each outlet, an outlet branch having at least one electronic switch whose conduction state is controlled either to transfer the signal from the inlet to the outlet, or else to reflect the signal; and
a shunt branch having at least one electronic switch which shunts the inlet signal to a load in the event of a loss of power to the electronic switches of the member.
Thus, in the event of a loss of power to the electronic switches, the input signal is diverted to a load, thereby protecting the elements which might be connected to the outlets such as filters or amplifiers. The switch element returns to normal operation after the power supply to the switches has been reestablished.
The invention also provides a switch matrix having n inlets and p outlets and comprising a plurality of such members.
In the event of a loss of power to the switches of the matrix of the invention, its outlets are no longer connected to the corresponding inlets, unlike what happens in a matrix of mechanical switches. Such a matrix can advantageously replace a matrix of mechanical switches since firstly a temporary loss at the outlets is generally without consequence, and secondly, and above all, it presents the advantage of mass and volume that are smaller. In addition, its cost can be considerably smaller.
In an embodiment of the switch member, the shunt branch has an electronic switch connected in series.
Preferably, in each outlet branch, an electronic switch is provided in shunt to form an open circuit when the corresponding outlet is selected and a short circuit otherwise, or in the absence of power.
To improve the short circuit, provision is made in each outlet branch for two electronic switches in parallel both controlled by the same bias.
During testing performed in the context of the invention, monolithic microwave integrated circuit (MMIC) technology switches have been made with two or three outlets and presenting losses limited to about 1.5 decibels (dB).
Thus, in another aspect, the invention provides a set of electronic switch members suitable for constituting a module for a switch matrix. In such a set or module, each inlet is connectable to a number r of outlets which is less than the total number of outlets.
In an embodiment, to make such modules, only two types of switch member are provided, one having two outlets and the other having three outlets.
It is preferable for the switch matrix to be such that it includes switch members arranged and connected in such a manner that when an inlet connected to one outlet is switched to another outlet, the losses due to the switch members passed through is the same both before and after switching.
In an embodiment, the electronic switches are microwave range integrated circuits.
The present invention also provides a switch matrix comprising a plurality of switch members.
In an embodiment, the matrix has n inlets and p outlets, where p is greater than n, each inlet being for connection to one out of r outlets and including for each inlet a set of associated switch members to present one inlet and r outlets.
In an embodiment, the matrix comprises, for each outlet, a set of switch members having r inlets and one outlet, the sets associated with the outlets being mounted the opposite way round to the sets associated with the inlets.
In an embodiment, the sets associated with the outlets are of structure analogous to the structure of the sets associated with the inlets.